Fix required for error- javax.crypto.BadPaddingException: Given final block not properly padded

Question

I am not sure what wrong I have done to this. To cut story short I want to decrypt a file with the given secretKey and using iv and I am using the following code to do so :

package com.Crypt.test;

import javax.crypto.Cipher;
import javax.crypto.Mac;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.security.MessageDigest;
import java.security.SecureRandom;

public class AES256CBCTest {
    static String encoding = "UTF-8";
    public static void main(String[] args) throws Exception {
        String key = "BURP6070";
        File inputFile = new File("/Users/jaynigam/Documents/workspace/EncryptDecrypt/files/test.xml.enc");
    try {
        BufferedReader br = new BufferedReader(new FileReader(inputFile));
        String st;
        File outputFile =null;
        FileOutputStream outputStream = null;
        try {
            while ((st = br.readLine()) != null){
                //decrypt(someString.getBytes(encoding), key);
                 String decrypted = decrypt(st.getBytes(), key);
                 outputFile = new File("/Users/jaynigam/Documents/workspace/EncryptDecrypt/files/decryptTest.xml.dec");
                 outputStream = new FileOutputStream(outputFile);
                    byte[] strToBytes = decrypted.getBytes(encoding);
                    outputStream.write(strToBytes);

            }

        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        finally {
            outputStream.close();
            br.close();
        }

    } catch (FileNotFoundException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
}
    //byte[] encrypted = encrypt(clean, key);



public static byte[] encrypt(String plainText, String key) throws Exception {
    byte[] clean = plainText.getBytes();

    // Generating IV.
    int ivSize = 16;
    byte[] iv = new byte[ivSize];
    SecureRandom random = new SecureRandom();
    random.nextBytes(iv);
    IvParameterSpec ivParameterSpec = new IvParameterSpec(iv);

    // Hashing key.
    MessageDigest digest = MessageDigest.getInstance("SHA-1");
    digest.update(key.getBytes());
    byte[] keyBytes = new byte[32];
    System.arraycopy(digest.digest(), 0, keyBytes, 0, keyBytes.length);
    SecretKeySpec secretKeySpec = new SecretKeySpec(keyBytes, "AES");

    // Encrypt.
    Cipher cipher = Cipher.getInstance("AES/CBC/NoPadding");
    cipher.init(Cipher.ENCRYPT_MODE, secretKeySpec, ivParameterSpec);
    byte[] encrypted = cipher.doFinal(clean);

    // Combine IV and encrypted part.
    byte[] encryptedIVAndText = new byte[ivSize + encrypted.length];
    System.arraycopy(iv, 0, encryptedIVAndText, 0, ivSize);
    System.arraycopy(encrypted, 0, encryptedIVAndText, ivSize, encrypted.length);

    return encryptedIVAndText;
}

public static String decrypt(byte[] encryptedIvTextBytes, String key) throws Exception {
    int ivSize = 16;
    int keySize = 16;

    // Extract IV.
    byte[] iv = new byte[ivSize];
    System.arraycopy(encryptedIvTextBytes, 0, iv, 0, iv.length);
    IvParameterSpec ivParameterSpec = new IvParameterSpec(iv);

    // Extract encrypted part.
    int encryptedSize = encryptedIvTextBytes.length - ivSize;
    byte[] encryptedBytes = new byte[encryptedSize];
    System.arraycopy(encryptedIvTextBytes, ivSize, encryptedBytes, 0, encryptedSize);

    // Hash key.
    byte[] keyBytes = new byte[keySize];
    MessageDigest md = MessageDigest.getInstance("SHA-256");
    md.update(key.getBytes());
    System.arraycopy(md.digest(), 0, keyBytes, 0, keyBytes.length);
    SecretKeySpec secretKeySpec = new SecretKeySpec(keyBytes, "AES");

    // Decrypt.
    Cipher cipherDecrypt = Cipher.getInstance("AES/CBC/NoPadding");
    cipherDecrypt.init(Cipher.DECRYPT_MODE, secretKeySpec, ivParameterSpec);
    byte[] decrypted = cipherDecrypt.doFinal(encryptedBytes);

    return new String(decrypted);
}
}

This returns me an output like ?lm:@?ڤ?w?)P@?\?s????Ka???0??{???w|k???o?\?. I have already tried UTF-8 decoding. But still no luck till now. Does anyone have any clue on this one?

Answer 1

I've had exactly the same problem as you, and also used the same source code! I had a problem using the return and input parameters as byte[], so i've converted it to String with Base64 encoding, so i didnt end up with problems with encodings.

My class:

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.nio.charset.StandardCharsets;
import java.security.MessageDigest;
import java.security.SecureRandom;
import java.util.Base64;


public class PasswordManager {

    private static final Logger LOGGER = LoggerFactory.getLogger(PasswordManager.class);
    private static final String key = "DdFfGg998012jffW"; // 128 bit key

    private PasswordManager() {
    }

    public static String encrypt(String plainText) {
        if (plainText == null) {
            return null;
        }

        byte[] clean = plainText.getBytes();

        // Generating IV.
        int ivSize = 16;
        byte[] iv = new byte[ivSize];
        SecureRandom random = new SecureRandom();
        random.nextBytes(iv);
        IvParameterSpec ivParameterSpec = new IvParameterSpec(iv);

        try {
            // Hashing key.
            MessageDigest digest = MessageDigest.getInstance("SHA-256");
            digest.update(key.getBytes(StandardCharsets.UTF_8));
            byte[] keyBytes = new byte[16];
            System.arraycopy(digest.digest(), 0, keyBytes, 0, keyBytes.length);
            SecretKeySpec secretKeySpec = new SecretKeySpec(keyBytes, "AES");

            // Encrypt.
            Cipher cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
            cipher.init(Cipher.ENCRYPT_MODE, secretKeySpec, ivParameterSpec);
            byte[] encrypted = cipher.doFinal(clean);

            // Combine IV and encrypted part.
            byte[] encryptedIVAndText = new byte[ivSize + encrypted.length];
            System.arraycopy(iv, 0, encryptedIVAndText, 0, ivSize);
            System.arraycopy(encrypted, 0, encryptedIVAndText, ivSize, encrypted.length);

            return Base64.getEncoder().encodeToString(encryptedIVAndText);
        } catch (Exception e) {
            LOGGER.error("Exception in decrypting a password. Returning null", e);
            return null;
        }
    }

    public static String decrypt(String encryptedString) {
        if (encryptedString == null) {
            return null;
        }

        byte[] encryptedIvTextBytes = Base64.getDecoder().decode(encryptedString);
        int ivSize = 16;
        int keySize = 16;

        // Extract IV.
        byte[] iv = new byte[ivSize];
        System.arraycopy(encryptedIvTextBytes, 0, iv, 0, iv.length);
        IvParameterSpec ivParameterSpec = new IvParameterSpec(iv);

        // Extract encrypted part.
        int encryptedSize = encryptedIvTextBytes.length - ivSize;
        byte[] encryptedBytes = new byte[encryptedSize];
        System.arraycopy(encryptedIvTextBytes, ivSize, encryptedBytes, 0, encryptedSize);
        try {
            // Hash key.
            byte[] keyBytes = new byte[keySize];
            MessageDigest md = MessageDigest.getInstance("SHA-256");
            md.update(key.getBytes());
            System.arraycopy(md.digest(), 0, keyBytes, 0, keyBytes.length);
            SecretKeySpec secretKeySpec = new SecretKeySpec(keyBytes, "AES");

            // Decrypt.
            Cipher cipherDecrypt = Cipher.getInstance("AES/CBC/PKCS5Padding");
            cipherDecrypt.init(Cipher.DECRYPT_MODE, secretKeySpec, ivParameterSpec);
            byte[] decrypted = cipherDecrypt.doFinal(encryptedBytes);

            return new String(decrypted);
        } catch (Exception e) {
            LOGGER.error("Exception in decrypting a password. Returning null", e);
            return null;
        }

    }

}

Also try using a key with the same length as mine, try that first, as it could be the problem. After try to use Base64 on string operations on your while loop.

Hope it helps you.